i
Ana Paula Piovezan Fugolin
Análise das Propriedades Físico-Químicas de Compósitos
Auto-Adesivos e Bulk-Fill
Analysis of Physical-Chemical Properties of Self-Adhering
and Bulk-Fill Composites
Piracicaba
2015
iii
Universidade Estadual de Campinas
Faculdade de Odontologia de Piracicaba
Ana Paula Piovezan Fugolin
Análise das Propriedades Físico-Químicas de Compósitos
Auto-Adesivos e Bulk-Fill
Analysis of Physical-Chemical Properties of Self-Adhering and
Bulk-Fill Composites
Tese apresentada à Faculdade de Odontologia de Piracicaba da Universidade Estadual de Campinas como parte dos requisitos exigidos para a obtenção do título de Doutora em Materiais Dentários.
Thesis presented to Piracicaba Dental School, State University of Campinas in partial fulfillment of the requirements for the degree of PhD in Dental Materials.
Orientador: Prof. Dr. Simonides Consani
Este exemplar corresponde à versão final da tese defendida por Ana Paula Piovezan Fugolin e orientada pelo Prof. Dr. Simonides Consani.
_______________________________ Assinatura do Orientador
Piracicaba 2015
vii
RESUMO Novos compósitos bulk-fill, autoadesivos e de menor contração foram desenvolvidos propondo mudanças na técnica restauradora incremental preconizada. Os objetivos desta pesquisa foram: 1) analisar os compósitos Tetric EvoCeram Bulk Fill (TEC), Surefil SDR (SDR), Vertise Flow (VF), Filtek Low Shrinkage (SIL) e compará-los com o compósito convencional Z100 (Z100) quanto à contração volumétrica, tensão de contração, grau de conversão, cinética, resistência à flexão e módulo de elasticidade; 2) avaliar a profundidade de polimerização e a resistência da união à tração de cavidades de Classe II restauradas com diferentes técnicas e diversas associações de materiais submetidas à ciclagem mecânica; e 3) analisar a adaptação marginal por microscopia eletrônica de varredura de restaurações de Classe II antes e após ciclagem mecânica e resistência coesiva. No capitulo 1, a contração volumétrica foi avaliada por dilatômetro de mercúrio e bonded disc (n=5) e a tensão de contração com Bioman (n=5). O grau de conversão foi analisado com espectroscopia de infravermelho próximo (NIR) (n=5) e a cinética por meio de optical bench (n=5). Resistência à flexão e módulo de elasticidade foram mensurados em ensaio com três pontos de apoio após 10 e 60 minutos da fotoativação. Os dados foram analisados por ANOVA e teste de Tukey (5%). VF apresentou os maiores valores de contração volumétrica e tensão de contração, enquanto que SIL obteve os menores. SDR apresentou a maior taxa de polimerização e os maiores valores de grau de conversão. VF apresentou os maiores valores de resistência à flexão após 10 e 60 minutos e Z100 os maiores valores de módulo de elasticidade. No capítulo 2, cavidades de Classe II ocluso-distais em terceiros molares humanos extraídos foram restauradas usando sistema adesivo convencional – XP Bond (XP) ou à base de silorano (SSA) associado aos compósitos TEC, SDR, VF, SIL e Z100 inseridos por meio da técnica incremental (I) e bulk (B). Os grupos experimentais testados foram: XP-Z-B, XP-Z-I, Z-B, Z-I, XP-TEC-B, XP-TEC-I, XP-SDR-Z100, SDR-Z100, VF-Z-B e SSA-SIL-B (n=8). Metade do total das amostras foi preparada para obtenção de palitos e submetida ao teste de resistência da união à microtração após sete dias de armazenagem, enquanto outra metade foi submetida à ciclagem mecânica antes do ensaio de resistência da união. A profundidade de polimerização foi mensurada em restaurações com 4,0 mm de
viii
profundidade removidas da cavidade e submetidas ao ensaio de dureza Knoop (n=3). Os resultados foram analisados por ANOVA e teste de Tukey (5%). Quanto à resistência de união o grupo XP-SDR-Z apresentou os maiores valores em ambas as superfícies (oclusal e cervical) nos grupos ciclados ou não. Os menores valores foram exibidos por VF-Z-B em ambas as superfícies para os grupos não ciclados e SSA-SDR-Z para os ciclados. Em relação à profundidade de polimerização, VF apresentou a maior redução da dureza, enquanto os demais compósitos apresentaram valores de redução menores do que 20%. No capítulo 3, as cavidades de Classe II restauradas seguiram as mesmas etapas dos grupos experimentais apresentados no capítulo 2 (n=5) e foram submetidas ao ensaio de ciclagem mecânica; porém, foram previamente moldadas para obtenção de replicas para análise da integridade marginal em microscopia eletrônica de varredura. As imagens foram analisadas pelo software Image J para verificar a porcentagem de fendas. Os compósitos utilizados para restaurar as cavidades foram submetidos ao teste de resistência coesiva (n=5). Os resultados foram analisados por ANOVA e teste de Tukey (5%). A análise da adaptação marginal qualitativa e quantitativa mostrou alteração significativa antes e após a ciclagem mecânica apenas para todos o grupo SSA-Z-B. Os resultados de resistência coesiva mostraram que Z100, SDR e SIL apresentaram os maiores valores, seguido de TEC. VF apresentou os menores valores. Concluiu-se que os novos compósitos apresentam propriedades comparáveis e, em algumas situações, melhores quando comparado ao compósito convencional.
Palavras-Chave: compósitos bulk fill, materiais auto-adesivos, materiais a base de silorano, propriedades físico-químicas.
ix
ABSTRACT New bulk-fill, self-adhering and low shrinkage materials were developed and purposed significant changes in the preconized incremental restorative technique. The aims of this research were: 1) analyze the new composites represented by Tetric EvoCeram Bulk Fill (TEC), Surefil (SDR), Vertise Flow (VF), Filtek Low Shrinkage (SIL) and compare them with the conventional composite Z100 (Z100) in relation to volumetric shrinkage, stress of polymerization, degree of conversion, kinetics, flexural strength and modulus; 2) evaluate depth of cure of different composites and microtensile bond strength of Class II cavities filled by different restorative techniques and materials association submitted to mechanical fatigue-cycling test; and 3) analyze marginal adaptation by scanning electron microscopy (SEM) of Class II restoration before and after mechanical cycling, and ultimate tensile strength. In the charter 1, the volumetric shrinkage was evaluated by mercury dilatometer and bonded-disc techniques (n=5) and stress of polymerization by Bioman instrument (n=5). Degree of conversion was analyzed with NIR-spectroscopy (n=5) and the kinetics by the optical bench (n=5). Flexural strength and modulus were carried out using a three-point bending test after 10 and 60 minutes after photocuring. Results were analyzed by ANOVA and Tukey’s test (5%). VF showed the highest values of volumetric shrinkage and stresses of polymerization and SIL the lowest ones. SDR obtained the highest rate of polymerization and the highest degree of conversion values. VF presented the highest values of flexural strength in both tested times, and Z100 the highest values of modulus. In the charter 2, Class II occluso-distal cavities (6 x 2 x 4 mm) in extracted human molars were restored using a etch-and-rinse adhesive system – XP Bond (XP) or silorane-based (SSA) associated to TEC, SDR, VF, SIL and Z100 composites placed by incremental (I) or bulk (B) technique. The tested experimental groups were: XP-Z-B, XP-Z-I, SSA-Z-B, SSA-Z-I, XP-TEC-B, XP-TEC-I, XP-SDR-Z100, SSA-SDR-Z100, VF-Z-B e SSA-SIL-B (n=8). Half of the samples were prepared to obtain sticks and submitted to the microtensile bond strength test after 7 days of storage. The other samples were submitted to the mechanical fatigue-cycling test before the microtensile bond strength test. Depth of cure was carried out in restorations with 4.0 mm of depth, removed and submitted to Knoop hardness test (n=3). Results were statistically analyzed by ANOVA and Tukey’s test (5%).
x
In relation to microtensile bond strength, in overall, XP-SDR-Z showed the highest values in both analyzed surfaces (occlusal and cervical) in cycling and no-cycling groups. The lowest values were exhibited by VF-Z-B in both analyzed surfaces in no-cycling groups and SSA-SDR-Z in cycling groups. In relation to depth of cure, VF obtained the lowest top-to-bottom ratio, while the other tested composites exhibited less than 20% of reduction. In the charter 3, Class II cavities were prepared following the same steps described in charter 2 (n=5) and were carried out to mechanical fatigue-cycling test. However, impressions were made before and after to obtain replicas to SEM analysis of the marginal integrity. The micrographs were analyzed by Image J software to measure the discontinuity percentage. The composites used in the cavities were submitted to the ultimate tensile strength (UTS) (n=5). Results were statistically analyzed by ANOVA and Tukey’s test (5%). Marginal adaptation analysis did not show significant alteration before and after cycling for all groups except to SSA-Z-B where cracks and gaps were found in the adhesive interface. In relation to UTS results Z100, SDR and SIL showed the highest results, followed by TEC. VF exhibited the lowest values. It is possible to conclude that new composites show comparable properties and in some situation better than conventional material.
Key words: bulk fill composites, self-adhering materials, silorane-based materials, physico-chemical properties
xi SUMÁRIO DEDICATÓRIA - - - xiii AGRADECIMENTOS - - - xv INTRODUÇÃO - - - 1 CAPÍTULO 1: - - - 5 CAPÍTULO 2: - - - 25 CAPÍTULO 3: - - - 45 CONCLUSÃO - - - 61 REFERÊNCIAS - - - 62 APÊNDICE - - - - - - 65 ANEXO 1 - - - 72
xiii DEDICATÓRIA
Aos meus pais Ilma Piovezan Fugolin e Paulo Fugolin, que sempre colocaram como meta de suas vidas proporcionar boa educação e formação para mim e minha irmã. Sei que deixaram de fazer muitas coisas para que hoje eu pudesse estar aqui. Nunca poderei agradecê-los suficientemente por tudo que fizeram e continuam fazendo por mim. Esse título é uma conquista de vocês.
A Deus, por me conceder todas as condições necessárias para eu lutar pelos meus objetivos, abençoando-me e colocando no meu caminho pessoas incriveis que fizeram a minha caminhada ser mais feliz e suave.
À minha irmã Mariana e ao meu cunhado Adriano, por sempre apoiarem as minhas decisões e me incentivarem na busca dos meus sonhos, vibrando comigo a cada conquista. Aos meus sobrinhos Guilherme e Maria Eduarda, por fazerem minha vida mais suave e doce
xv
AGRADECIMENTOS
Ao meu orientador Prof. Dr. Simonides Consani, um exemplo de competência e responsabilidade. Agradeço os ensinamentos transmitidos, o incentivo constante ao meu crescimento e as diversas oportunidades ao longo desses seis anos que me proporcionaram amadurecimento profissional e pessoal. Obrigada por conceder a mim o prazer e a honra de ser sua orientada.
Ao meu orientador no exterior Prof. Dr. Jack Liborio Ferracane, uma das pessoas mais fantásticas que já conheci. Além de toda paciência, cuidado e carinho que teve comigo durante o estágio em Portland, ensinou-me que ao ser um ícone na área de conhecimento, pode-se também conservar a humilde para tratar a todos como iguais. Aprendi nesse período mais do que os ensaios mecânicos, as formas de redigir um artigo e como conduzir uma pesquisa. Aprendi que trocar lâmpadas do laboratório, sujar as mãos de graxa para ajustar uma máquina e lavar vidraria de laboratório só concebem à pessoa mais dignidade e admiração.
À Profa. Dra. Carmem Pfeifer, pela colaboração neste trabalho e por todo o carinho que me proporcionou durante o meu estágio em Portland. Pessoa maravilhosa, esforçada e inteligiente, além de inspiração para todos que estão na carreira acadêmica.
À Profa. Dra. Fernanda Gwinner, que se tornou uma grande amiga. Profissional dedicada que não mediu esforços para me ajudar em todos as ocasiões. Foi a pessoa que me proporcionou o referencial de família no exterior e que me fez sentir em casa, mesmo estando há milhares de quilômetros de Piracicaba.
Aos Profs. Drs. Manoel Macedo, Juliana da Costa, Thomas Hilton, David Mahler e Harry Davis, pela acolhida e por todo esforço não poupado para me ajudar na execução deste trabalho.
À Faculdade de Odontologia de Piracicaba da Universidade Estadual de Campinas, em nome do Diretor Prof. Dr. Guilherme Elias Pessanha Henriques e Diretor Associado Prof. Dr. Francisco Haiter Neto.
Aos docentes da Área Materiais Dentários, Prof. Dr. Mário Fernandes de Goes e Prof. Dr. Lourenço Correr Sobrinho, pelos ensinamentos determinantes na minha formação professional; Prof. Dr. Américo Bortolazzo Correr, por todo apoio durante esses anos de convivência no
xvi
laboratório, um profissional ético e pessoa carismática e gentil; e Prof. Dr. Mário Alexandre Coelho Sinhoreti, pela participação fundamental durante minha pós-graduação, sempre sensato e pronto para ajudar em tudo que eu precisasse.
Ao ex-coordenador do Programa de Pós-graduação em Materiais Dentários Prof. Dr. Marcelo Giannini, pelo empenho e dedicação em submeter este projeto à solicitação de bolsa para estágio no exterior. Mesmo com diversos encargos nas atividades que desenvolve, não mediu esforços para assumir a responsabilidade de ser o contato com o exterior e viabilizar minha ida para Portland.
Á CAPES pela concessão da bolsa que possibilitou o estágio no exterior.
Aos funcionários do Laboratório de Materiais Dentários Engenheiro Marcos Blanco Cangiani e Técnica Selma Aparecida Barbosa Segalla, verdadeiros exemplos de dedicação. Agradeço pela simpatia e pelo auxílio prestado no decorrer do Programa. E ao Técnico do Laboratório de imagens eletrônicas Biólogo Adriano Luis Martins, pela atenção e orientação no uso do microscópio eletrônico de varredura (MEV).
Aos alunos do Programa Ariene Arcas Leme, Giovana Araújo, Guilherme Guarda, Roberta Galetti, Tatiany Araújo, Isadora Guimarães, Carlos Oliveira Junior, Ailla Lancellotti, Andréia Bolzan e Ravana Sfalcin, amigos essenciais durante todos esses anos. Não consigo imaginar como seria minha vida sem o apoio e carinhosa presença de vocês. Com certeza hoje sou um pouquinho de cada um de vocês.
Às minhas amigas de Graduação Marina Passarella Desjardins, Marília Arnoni e Tatiane Soave, por dividirem comigo todo os momentos bons e ruins, de sucesso e fracasso e de alegria e tristeza.
À querida amiga Ana Elisa Saboya Soler, que por fazer parte da minha vida está sempre disposta a me ajudar e ouvir. E à Lívia Aguilera Gaglianone, por tornar minha experiência de morar fora mais especial e feliz.
xvii
Se você quer um pedacinho do Paraíso, acredite em Deus. Mas se você quer conquistar o mundo, acredite em você porque Deus já te deu tudo o que você precisa
para você vencer. Augusto Branco
1
INTRODUÇÃO
A formulação dos compósitos tem evoluído consideravelmente desde que esses materiais foram introduzidos na Odontologia na década de 1960 ¹. No início da evolução, as mudanças mais importantes estavam vinculadas as partículas de carga; porém, atualmente o foco tem sido a matriz orgânica, visando, principalmente, o desenvolvimento de sistemas com reduzida contração de polimerização que, consequentemente, podem gerar menor tensão de contração nos compósitos e materiais autoadesivos ¹.
Os compósitos autoadesivos representam nova categoria de material recentemente introduzida no mercado e que, de acordo com instruções dos fabricantes, não requerem tratamento prévio do substrato2. Esses materiais são compostos por monômeros mais ácidos que reagem com o substrato e se infiltram na estrutura do dente, resultando em retenções micromecânicas potencialmente reforçadas por interação química adicional 2,3. Portanto, trata de materiais que visam a facilitar e simplificar a técnica restauradora; porém, espera-se desses materiais menor desempenho no que diz respeito à adesão quando comparado aos sistemas convencionais 2. Esse fato ocorre porque o material é mais viscoso, enquanto que os adesivos convencionais são mais fluidos e conseguem promover melhor interação com o substrato 2. Nessa nova categoria de compósitos encontra-se disponível no mercado o Vertise Flow (Kerr Dental, Orange, CA, USA) que, segundo o fabricante, pode ser utilizado para forramento de cavidades de Classes I ou II, para selamento de fóssulas e fissuras, reparos em cerâmica e restauração de cavidades de Classes I ou II pequenas 4. Porém, existem poucas informações na literatura que permitam caracterizar esse material e predizer o desempenho clínico.
No que diz respeito às estratégias para reduzir a contração volumétrica e minimizar as tensões geradas durante a contração de polimerização foram desenvolvidos os compósitos à base de silorano 5. Esses materiais são compostos pela combinação de siloxano que confere características hidrófobas ao material e por anéis oxirano cicloalifáticos que se abrem durante a polimerização causando expansão 5. Teoricamente, esses materiais apresentam menores contração volumétrica e tensão de contração, sem comprometer as propriedades mecânicas 5,6. Porém, alguns dados apresentados na literatura são contraditórios e
2
inconclusivos. Assim, um trabalho mostra que esse material apresenta menor contração volumétrica sem interferir na quantidade de tensões geradas 7 e outro defende que materiais à base de silorano geram menor quantidade de tensões quando comparado aos materiais à base de metacrilato 8.
Entretanto, compósitos à base de silorano requerem a utilização de sistema adesivo específico também à base de silorano. Por se tratar de categorias diferentes de polímeros, acredita-se existir incompatibilidade desses adesivos com os compósitos à base de metacrilato. Entretanto, os resultados mostraram que essa combinação poderia ser promissora 9.
Mesmo com a evolução dos compósitos, a técnica restauradora foi pouco modificada. A inserção em pequenos incrementos tem sido ainda largamente preconizada com a intenção de minimizar as tensões de contração10, promover maior grau de conversão e obter adequada adaptação marginal 11. Na tentativa de facilitar o procedimento clínico, diminuir o tempo restaurador e reduzir as tensões de contração foram desenvolvidos compósitos que, segundo os fabricantes, podem ser inseridos em incrementos mais espessos. Um deles é o SDR Posterior Bulk Fill Flowable Base (Dentsply, Konstanz, Germany), introduzido no mercado como compósito de menor viscosidade, podendo ser aplicado em incrementos de até 4 mm e recoberto por camada de aproximadamente 2,0 mm de compósito convencional 11
. Outro compósito similar é o Tetric EvoCeram Bulk Fill (Ivoclar-Vivadent, Schaan, Liechtenstein) que, conforme alegado pelo fabricante, pode ser utilizado em bloco na técnica restauradora e também inserido em camadas de até 4 mm, gerando menor quantidade de tensões de contração e propriedades mecânicas satisfatórias 12. Entretanto, são ainda escassas as informações encontradas na literatura sobre esses materiais.
As tensões geradas durante a contração de polimerização e a contração volumétrica são apontadas na literatura como uma das principais causas de falha da adesão 13, sendo parâmetros importantes para a avaliação do desempenho clínico desses materiais poliméricos. Contudo, parece existir relação entre as tensões geradas durante a contração de polimerização e a taxa de polimerização; porém, os resultados mostrados na literatura são controvertidos 13, havendo trabalhos que mostram que reduções significativas nas taxas de polimerização não correspondem necessariamente à redução significativa das tensões de
3
contração 7,14. Isso provavelmente ocorre pelo fato de que o desenvolvimento de tensões estaria relacionado não somente à contração de polimerização, mas também à taxa de polimerização e ao módulo de elasticidade do material14. Dessa forma, taxa de polimerização e módulo de elasticidade parecem ser fatores importantes para o completo entendimento da cinética do desenvolvimento de tensões durante a polimerização dos compósitos.
A resistência à flexão pode ser indicativa do desempenho e da longevidade dos compósitos quando submetidos às forças mastigatórias, estabelecendo o perfil do material em relação às propriedades mecânicas 15. Esse fato ocorre da mesma maneira do que no teste de resistência da união por microtração, frequentemente utilizado para avaliar a adesão entre substrato e sistema adesivo e entre sistema adesivo e material restaurador 16. A análise do grau de conversão permite avaliar a eficiência da polimerização e valores reduzidos de grau de conversão podem estar associados às propriedades mecânicas deficientes dos compósitos, menor resistência à fratura e ao desgaste e também ao aumento da citotoxicidade 17.
Adequada adaptação interna é apontada na literatura como um dos principais desafios para a Odontologia restauradora 18. Esta premissa ocorre porque muitos fatores contribuem para o desenvolvimento de fendas entre substrato e material restaurador. Dentre eles estão: diferenças no coeficiente de expansão térmica do dente e do material restaurador, adesão inadequada à dentina e contração de polimerização do material restaurador 18. Além desses fatores, as restaurações estão sujeitas às tensões mecânicas e alterações térmicas ocorridas na cavidade bucal, condições que contribuem significativamente para a deterioração da interface dente-material 17. Falhas na adaptação estão também vinculadas aos fenômenos como degradação, descoloração e pigmentação, cáries recorrentes, microinfiltração e hipersensibilidade, associação que reduz o tempo de vida útil da restauração 18.
Dessa forma, considerando a disponibilidade de novos compósitos que propõem inovações significativas nas técnicas restauradoras e a falta de evidências científicas na literatura, seria conveniente o estudo desses materiais e técnicas para avaliar a efetividade
4
no desempenho clínico, assim como a combinação entre técnicas restauradoras e diferentes materiais.
Considerando esse contexto, o objetivo neste estudo foi avaliar:
1. Os compósitos Z100, Tetric Evo Ceram Bulk Fill, SDR, Filtek Silorane e Vertise Flow quanto à contração volumétrica, tensão de contração, cinética, grau de conversão, resistência à flexão e módulo de elasticidade.
2. A profundidade de polimerização e a resistência da união resina-dentina por microtração em cavidades de Classe II restauradas com diferentes compósitos (Z100, Tetric Evo Ceram Bulk Fill, SDR, Filtek Silorane e Vertise Flow), utilizando sistemas diferentes adesivos (XP Bond e Silorane System Adhesive), diferentes técnicas restauradoras e ciclagem mecânica das restaurações;
3. A adaptação marginal de restaurações de Classe II antes e após a ciclagem mecânica por meio da microscopia eletrônica de varredura e a resistência coesiva dos compósitos Z100, Tetric Evo Ceram Bulk Fill, SDR, Filtek Silorane e Vertise flow.
5
CAPÍTULO 1
Analysis of physical-chemical properties of bulk-fill, self-adhering and low-shrinkage dental composites
Abstract
Objective: To determine flexural strength, modulus, kinetics, volumetric shrinkage, degree of conversion and stress of polymerization of bulk-fill, self-adhering and low-shrinkage dental composite materials.
Materials and methods: The materials used for this study were Z100 (Z100), Tetric EvoCeram Bulk Fill (TEC), Surefil SDR flow (SDR), Vertise Flow (VF), and Filtek Silorane (SIL). Light curing was carried out using a led unit with 1170mW/cm2. Degree of conversion (DC) was measured in real time with FT-NIR spectroscopy (n=5). Stress of polymerization (SP) was monitored using Bioman instrument. (n=5). Flexural strength (FS) and Modulus (M) were determined after 10 and 60 minutes using a three point bending test. Volumetric shrinkage (VS) was investigated using bonded-disc technique and mercury dilatometer (n=3), and kinetics reaction was monitored by optical bench (n=5). Data were analyzed using ANOVA and Tukey's test (α=0.05).
Results: DC showed the highest results for VF (76.04%) and SDR (65.92%). SIL, Z100 and TEC exhibited the lowest results (41.98, 45.76 and 46.74%, respectively). In relation to SP, VF obtained the highest values (20.04 MPa) and SIL the lowest ones (5.11 MPa). The highest values of FS were showed by VF in 10 and 60 minutes (78.80 and 101.00 MPa, respectively), and the other materials presented statistically similar results. Z100 exhibited the highest values of M in 10 and 60 minutes (9.59 and 11.24 GPa, respectively) while SDR the lowest ones (3.70 GPa). VS measured by mercury dilatometer and bonded-disc showed statistical similarity (p>0.05). VF was the material with the highest VS (3.65%)
6
and LS with the lowest values (0.66%). Analyzing reaction kinetics, SDR (8.90 %.s-1) showed the best results, followed by VF (5.53 %.s-1).
Conclusion: The tested materials showed different behaviors in relation to physic-chemical properties. SIL showed the lowest values for volumetric shrinkage and stress of polymerization. The highest flexural strength was showed by VF.
7 1. Introduction
Resin composite have been used in dentistry for nearly decades1. Since these materials were introduced to dentistry their composition has evolved significantly. But until recently, the most important changes have involved the particles filler, which has been reduced in size to produce materials with better mechanical properties2. Beside the important changes in filler amount, shape and surface treatment, changes in monomer structure or chemistry and modifications of dynamics of the polymerization reaction seem to be the most promising approaches3. Current changes are more focused on the polymeric matrix of the material, principally to develop systems with reduced polymerization shrinkages2 and to simplify the clinical application steps needed to bond the composite restoration to substrate4.
The most common resin composites are methacrylate-based. The predominant base monomer used in these dental composites has been Bis-GMA, which is mixed with other dimethacrylates, such as TEGDMA and UDMA5. During polymerization of this material, the formation of a polymer network results in a denser structure, leading to a volumetric shrinkage6. These composites require an enamel and dentin surface pretreatment using either an etch-and-rise or self-etch adhesive making rather complex and often very technique sensitive7. To simplify the clinical application and technique sensitivity, self-adhering composites were introduced in the market and the first product of this new generation to be launched was the Vertise Flow (Kerr Corporation), a flowable resin composite8. According to the manufacturer’s instructions, self-adhering composites do not require any pretreatment of the substrate4 and its self-adhesiveness would be based upon the use of acidic monomers that demineralize and simultaneously infiltrate the tooth substrate, resulting in micro-mechanical retention enhanced by additional chemical interaction4.
Few years ago, a new category of flowable resin composites called bulk-fill flowable composites was launched9. Surefil® SDR™ flow (Dentsply) is one of this composite category, and according to manusfacture’s intructions this material is designed to
8
be used as base in class I and II restorations placed in 4 mm increments with minimal polymerization stress10.
Tetric Evo-Ceram Bulk Fill (Ivoclar-Vivadent) is another bulk-fill material that according to manufacturer takes the effort out of posterior tooth restorations, can be used in increments of up to 4 mm, and shows low shrinkage stress11.
In order to reduce the rate of shrinkage stress manufacturers have invested their resources in the development of low-shrinkage restorative composites and, recently, a number of examples of these new materials is available for clinical use12. FiltekTM LS – Low Shrink Posterior (3M ESPE) is a low-shrinkage composite based on a silorane resin consisting of siloxane and oxirane functional molecules. However, shrinkage stress involves more than how much a composite shrinks in volume. Thus, other factors such as elastic modulus, volumetric shrinkage, filling and curing protocol, degree of conversion, cavity shape, remaining tooth and restorative technique can also be included in shrinkage stress considerations12.
Therefore, this study was intended to investigate these bulk-fill, self-adhering and low-shrinkage materials with respect to flexural strength, modulus, kinetics, volumetric shrinkage, degree of conversion and stress of polymerization of bulk-fill, self-adhering and low-shrinkage. The null hypothesis is that there would be no statistically differences in performance between the five resin composites tested.
2. Materials and Methods
9
Table 1: Investigated Restorative Materials and Their Composition According to Information Provided by the Respective Manufacturers
Composite (Abbreviation) Manufactures and Classification Components Lot Z100 (Z100) 3M ESPE Conventional
Organic matrix: Bis-GMA, TEGDMA
Filler Particles: 85 wt%, 66 vol% - silica, zirconia
N427925
Tetric EvoCeram Bulk Fill
(TEC)
Ivoclar Vivadent Bulk-Fill
Organic matrix: GMA, Bis-EMA, UDMA
Filler Particles: 80 wt%, 60 vol% - Barium glass, YbF3, mixed oxide,
PPF R49602 Surefil SDR flow (SDR) Dentsply Bulk-Fill
Organic matrix: Modified UDMA, EBPADMA, TEGDMA
Filler Particles: 68 wt%, 44 vol% - Ba-glass, Sr-glass
100506
Filtek Silorane Low Shrink Posterior Restorative (SIL) 3M ESPE Low-Shrink Organic matrix: 3,4- epoxycyclohexyl-ethyl-cyclo-poly-methylsiloxane, bis-3,4- epoxycyclohexyl-ethyl-phenyl-methylsilane
Filler Particles: 76 wt%, 55 vol% - SiO2, YbF3 N436469 Vertise Flow (VF) Kerr Corporation Self-Adhering
Organic matrix: GPDMA, HEMA, Bis-GMA
Filler Particles: 70 wt%, 48 vol% - prepolymers, silaneted Ba-glass, SiO2, YbF3
4675010
EBPDADMA ethoxylated bisphenol-A-dimethacrylate, TEGDMA triethylene glycol dimethacrylate, UDMA urethane dimethacrylate, GMA bisphenol-A-glycidyldimethacrylate, GPDMA glycerolprosphoric acid dimethacrylate, HEMA hydroxyethyl methacrylate, Bis-EMA bisphenol-polyethylene glycol dimethacrylate, YbF3 ytterbium trifluoride, SiO2 silicium oxide, Ba-glass barium glass, Sr-glass
10
2.1 Flexural Strength Test and Modulus of Elasticity
The measurement of flexural strength and modulus of the resin composites was carried out by the 3-point bending method. Bipartite matrix was used to made bars with 2x2x20 mm. Matrix was filled with only one increment of the resin composite and light-cured for 40 seconds using DEMITM Plus LED Curing Light (Kerr Corporation). The intensity of the light was checked periodically with a potentiometer to ensure that 1170 mW/cm2 was always delivered during the experiments. Ten samples were made for each composite. The surface of the sample was polished with 1,200 grit paper to create a glossy and flat surface. Five samples were tested after 10 minutes of the photocuring process and the other five after 1 hour. The measurements were performed using an universal testing machine (Model TT-B Universal Testing Instrument, Instron Engineering Corporation, Canton, MA) at a crosshead speed of 1 mm/s.
The flexural strength (FS) in MPa was calculated using the formula:
FS = 3 x F x l 2 x b x h2
Where F is the maximum load in Newtons exerted on the sample at the point of the fracture; l is the distance in mm between the supports (20 mm); b and h are, respectively, the width and thickness in mm of the sample. The modulus was given by the software.
2.2 Stress of Polymerization
A Bioman instrument was used to analyze the shrinkage-stress kinetics.
As previously described by Gonçalves et al, 201213, the system consisted of a cantilever load cell whose extremity is fitted to a rigid integral clamp on its free end. The clamp holds a 10 mm diameter and 22 mm tall steel rod vertically and perpendicular to the load cell axis. A 5-mm diameter, 1-mm tall steel rod was fixed at the center of the lower face of the standard rod with a cyanoacrylate adhesive to produce a rod substrate with a
11
reduced surface are to be consistent with that used in the other test systems. The opposite surface was a rigid fused silica glass plate of 3 mm thickness.
The surface of the silica glass plate was treated with a thin layer of silane ceramic primer (3M ESPE, St. Paul, MN, USA) and the surface of the piston with Z-Prime Plus (Bisco Inc., IL, USA).
The composite was then inserted into the 1-mm gap between the upper rod and the lower glass slide and shaped into a cylinder. The samples were light-cured through the glass using a DEMI LCU in 46.8 J/cm2 (1170 mW/cm2 for 40 s) with a special tip (n=5). Data were registered for 10 min by a computer and the final shrinkage-stress calculated.
2.3 Volumetric shrinkage
The volumetric shrinkage was measured by two methods, Mercury Dilatometer and Bonded-Disc technique. This occurred because the two composites tested, SDR and VF, are flowable materials making impossible the test in the Mercury Dilatometer.
2.3.1 Mercury Dilatomer
Composite volumetric shrinkage was carried out in a mercury dilatometer (ADA Health Foundation, Gaithersburg, MD, USA). For this, approximately 0.1 g of composite was placed on a glass slide previously sandblasted and treated with silane ceramic primer (3M ESPE, St. Paul, MN, USA). A glass column was clamped to the glass slide, filled with mercury and a LVDT (linear variable differential transducer) probe was placed on top of the mercury column.
The composite was light-cured from underneath, through the glass slide using a QTH unit (QHL75, Dentsply) with a radiant exposure of 18 J/cm2. The data was recorded during a total period of 60 min. The volumetric shrinkage was calculated using the LVDT probe readings and previously recorded mass and density values. Five samples were tested for each composite (n=5).
12 2.3.2 Bonded-Disc Technique
This analysis was made according to Bryant & Mahler, 200714.
The bonded-disc technique consisted of a 3 mm-thick glass plate, a thin circular metal ring (16.6 mm inner diameter, 18.9 mm outer diameter, and 0.20 to 0.60 mm thick) and a thin round glass microscope coverslip (0.22 mm diameter and 0.16 mm thick). The surfaces of the glass components that contacted the samples were sandblasted.
The metal ring was placed onto the glass plate, the resin composite was inserted on the central region of the glass plate inside the metal ring, the coverslip was placed, and a force was applied make contact between coverslip and metal ring.
The components were placed beneath an LVDT device with the transducer core placed on the flexible coverslip. The output of the LVDT was connected to a mV recorder which recorded the coverslip deflection in µm vs. time. The samples were light-cured for 40 seconds with the DEMI light-curing unit (n=5).
Volumetric shrinkage was determined to be the deflection of the glass coverslip and the variation of the voltage according to the formula:
% Shrinkage =
Where is the difference between initial and final voltage, and is the difference between initial and final height of the sample.
2.4 Degree of Conversion
Degree of conversion of the resin composites was carried out with a Fourier Transformed Near-Infrared (NIR) Spectroscopy (Nicolet 6700 FTIR, Thermo Scientific, Pittsburgh, PA, USA). Disc-shaped samples were made using silicone rubber molds (n = 5; Ø = 6.5 mm; h = 0.8 mm) sandwiched between glass slides and photoactivated for 40 seconds. After 24 hours, NIR spectra were recorded in the absorbance mode. Degree of conversion was determined by calculation the variation in intensity of the methacrylate peak at 6165cm-1 and 4625 cm-1 to Z100, TEC, SDR and VF, and peaks near the epoxy
13
region at 4581 cm-1 and 4071 cm-1 were selected to SIL. Two spectra per sec were collected with 4 cm-1 resolution and three spectra were obtained before of the light-curing process and used as a reference. The degree of conversion was calculated according to the formula:
2.5 Reaction Kinetics
Reaction Kinetics was monitored by an optical bench for 10 minutes. According to Howard B et al, 201015 in this technique stable and repeatable orientation and alignment of the specimen, curing light and analytical instrumentation were facilitated with an optical bench fitted with a collimating lens on the NIR output fiber, which focused the NIR signal through the mounted sample to a condensing lens that maximized signal collection for the NIR return fiber. The visible light intensity transmitted through the sample was monitored after passing through a calibrated neutral density filter, an aperture to exclude stray light and finally into the UV–Vis fiber optic inlet. With this test, it is possible to determine the vitrification point and maximum rate of polymerization (n=5).
2.6 Statistical Analysis
For stress polymerization, volumetric shrinkage, degree of conversion and kinetics, a statistical evaluation was performed with One-Way ANOVA and Tukey's test at a 5% level of significance. For flexural strength, modulus and volumetric shrinkage, the statistical analysis was performed with Two-Way ANOVA and Tukey’s test at a 5% level of significance.
14
Descriptive statistics for flexural strength and modulus are presented in Table 2. All composites showed statistically significant increase of flexural strength after 60 minutes. VF recorded the highest (p<0.05) mean flexural strength in both tested times.
In relation to modulus, only TEC and SDR exhibited statistically significant difference (p<0.05) between 10 and 60 minutes. Z100 recorded the highest mean in both times and SDR the lowest ones in both tested times.
Table 2. Average of flexural strength (MPa) and Modulus (GPa) with respective standard deviations, after 10 and 60 minutes
Flexural Strength Modulus
Composites
10 min 60 min 10 min 60 min
Z100 65.30 (10.39) Bb 68.91 (15.29) Ab 9.59 (0.87) Aa 11.24 (2.74) Aa
TEC 52.22 (10.60) Bb 66.83 (12.27) Ab 4.46 (0.62) Bc 6.52 (0.58) Abc
SDR 54.29 (9.57) Bb 68.99 (9.73) Ab 1.75 (0.52) Bd 3.70 (0.27) Ad
VF 78.80 (14.75) Ba 101.00 (9.09) Aa 4.12 (0.40) Ac 5.49 (0.65) Ac
SIL 61.24 (12.10) Bb 72.49 (9.31) Ab 6.09 (0.53) Ab 8.11 (0.44) Ab Means followed by different letters (upper in row and lower in column) showed statistically significant difference (p≤0.05).
The results of polymerization stress, volumetric shrinkage and degree of conversion are described in the Table 3. VF showed the highest means of polymerization stress (20.04 ± 0.54) followed by Z100 (16.69 ± 0.31), TEC (10.54 ± 0.40) and SDR (8.54 ± 0.55). SIL recorded the lowest results (5.11 ± 0.50).
VF showed the highest volumetric shrinkage results (3.65 ± 0.23), followed by Z100 (2.41 ± 0.03), TEC (2.44 ± 0.07) and SDR (2.34 ± 0.07) that recorded similar results. The lowest results were presented by SIL (0.66 ± 0.21).
The results of degree of conversion indicated a significant difference among tested resin composites. SDR presented the highest values (76.04 ± 4.36) followed by VF (65.92 ± 3.11). SIL (41.98 ± 1.84), Z100 (45.76 ± 2.36) and TEC (46.74 ± 1.89) recorded the lowest similar results.
15
Table 3. Average of stress of polymerization (MPa), volumetric shrinkage (%) and degree of conversion (%) with respective standard deviations
Volumetric Shrinkage Composites Polymerization
Stress Dilatometer Mercury Bonded Disc
Degree of conversion Z100 16.69 (0.31) b 2.54 (0.02) aA 2.41 (0.03) bA 45.76 (2.36) c TEC 10.54 (0.40) c 2.33 (0.03) aA 2.44 (0.07) bA 46.74 (1.89) c SDR 8.54 (0.55) d NA 2.34 (0.07) b 76.04 (4.36) a VF 20.04 (0.54) a NA 3.65 (0.23) a 65.92 (3.11) b SIL 5.11(0.50) e 0.72 (0.04) aA 0.66 (0.21) cA 41.98 (1.84) c Means followed by different letters (upper in row and lower in column) show statistically significant difference (p≤0.05)
Kinetics reaction results are described in the Table 4. SDR recorded the highest values (8.9 ± 0.8) of maximum rate of polymerization followed by VF (5.5 ± 0.9). Z100 and TEC showed the lowest and similar results (2.8 ± 0.2 and 2.5 ± 0.9, respectively).
Table 4. Maximum rate of polymerization (%.s-1) and vitrification point (%) average with respective standard deviations
Composites
Maximum rate of
polymerization Vitrification Point
Z100 2.8 (0.2) c 7.2 (1.6) c
TEC 2.5 (0.9) c 10.1 (1.1) bc
SDR 8.9 (0.8) a 26.0 (3.0) a
VF 5.5 (0.9) b 14.1 (2.2) b
SIL NA NA
Means followed by different letters in each column show statistically significant difference (p≤0.05).
16 4. Discussion
Large and significant differences (p<0.001) were observed for all considered physical-mechanical properties for the tested composite, which led to the rejection of the null hypothesis.
Flexural Strength and Modulus
According to this work, the flexural strength of the TEC and SIL bulk-fill composites are closer to those of the SDR flowable materials and Z100 conventional composite. This result is in agreement with previous study16.
The positive correlation between flexural strength and modulus and filler mass fraction is also in accordance with previous works3,17 but not in another where the influence of the organic matrix was more prominent18. Differences in flexural strength and modulus may be due to specificities of the organic matrix, such as variations of filler size and morphologies, monomer type and ratio or photoinitiation chemistries18. The VF self-adhering flowable composite suffered the greatest of the flexural strength values. This can be related to the inorganic content. According to manufacturer, VF consists of 4 filler types: barium glass filler (10 µm), pre-polymerized filler (20 µm), nano-sized colloidal silica (10-40 nm) and nano-sized Ytterbium fluoride filler ((10-40 nm) totaling 70 wt% and resulting in high flexural strength19. On the other hand, pre-polymerized filler (PPF) would be responsible for smooth and flexibility characteristics of this material, explaining the low modulus.
Z100, SDR, TEC and SIL showed similar values of flexural strength. Although previous studies20,21 the bulk-fill materials exhibited lower mechanical properties compared with the conventional composites, it should be noted that certain properties of the bulk-fill may be equivalent or very similar to conventional materials. This performance of low-shrinkage and bulk-fill materials would be attributed to modifications of monomers and filler contents, and addition of polymerization modulators and initiation boosters resulting in materials with improved properties22.
17
The lowest modulus showed by SDR can be related to composition. The manufacturer renounced to bisphenol-A-dimethacrylate (Bis-GMA) and formed the organic matrix out of other dimethacrylates10, 23. This way, the SDR is supposed to be less viscous because UDMA, TEGDMA and ethoxylated EBPDMA form more flexible polymers than Bis-GMA21. On the other hand, Z100 showed the highest modulus. This result may be due to the combination of Bis-GMA and TEGDMA in its matrix as well as its higher filler content. Asmussen and Peutzfeldt24 found that the combination of 50% Bis-GMA, 50% TEGDMA in organic matrix, and 0% UDMA is responsible for the highest elastic modulus.
Tested composites showed higher results of flexural strength and modulus after 60 minutes time. This can be explained by a continuous polymerization reaction even after the photocuring process. On the bottom, a slower polymerization reaction could be noted. This way, during the next minutes after the stopping of the photocuring occurs the activation of the camphorquinone, induction of polymerization nucleus, and formation of longer polymer chains, resulting in better properties25. And according to Burstcher26, even a small increase in the extent of degree of conversion near the end of the polymerization process can largely affect the density of cross-linking in the polymer network, and thus the mechanical properties of resin composites.
Degree of conversion
SDR showed the highest values of DC (76.06%). This value is in agreement with previous study27. The curing efficiency of SDR was found to be overall satisfactory and this result is in according to the findings of previous investigations23,27,28. The peculiar photoinitiating system may have contributed to such outcome21. SDR features a photoactive group embedded in urethane-based methacrylate monomers and capable of interacting with camphorquinone10. Such interaction, claimed to modulate curing for stress control purposes, might also have resulted in deeper polymerization25. Beside the photoinitiating system, also the optical properties might have had a significant role in this regard. Specifically, the translucency of SDR is expected to favor light penetration, thus enabling increased degree of conversion27.
18
Comparing out results of previous study29, VF showed similar values of degree of conversion. Since no definitive information is available about its chemical composition, it is difficult to draw an accurate explanation. However, a reasonable reason is based on the viscosity of this composite. VF shows flow consistency that is probably due to the high ratio of low molecular weight monomers with high mobility and, than, high degree of conversion.
Z100, TEC and SIL obtained similar results. This is according to previous study, where TEC showed similar degree of conversion when compared to the tested conventional composite30. Filler inorganic particles of these materials might be one reason for this result. All of them show very similar percentage and sizes of filler content and according to literature the inorganic particles can interfere in the mobility of reactive sites and actively participate in the scattering phenomena of the light, defining the degree of conversion30.
Due to different organic and filler compositions of the composites, mechanical superiority cannot be predicted by degree of conversion. Together with a different filler loading and filler type, each monomer associated to additional group can imply in different properties in different molecular architecture29. Thus, a high DC in the case of VF and SDR does not necessarily mean similar mechanical values as reflected in the mechanical properties measured in this study.
Kinetics
Important characteristics of the composites, as vitrification point and rate of polymerization can be studied by analyzing the polymerization reaction. Vitrification point is the degree of conversion at the maximum rate of polymerization. Defines the point in conversion at which diffusion limitations dramatically decrease rate of polymerization and ultimately influences final degree of conversion and stress development within the material. The vitrification point marks the point in conversion at which diffusional limitations preclude propagation of reactive agents. After the vitrification point, the reaction undergoes deceleration. Past that point, the material is no longer capable of relieving polymerization stress31.
19
The higher the conversion at vitrification, the better the material can accommodate polymerization stress. SDR presented the highest DC@Rpmax among all materials. Interestingly, SDR was also the material with the higher value of Rpmax, showing that higher rates of polymerization do not always translate into higher polymerization stress.
Considering that there was too much “noise” in the silorane reaction kinetics, it was not possible to obtain data about Rpmax and vitrification point. But analyzing these reactions it is possible to see that some change in monomer area starts 40 seconds after the photocuring process. This way, we can suppose that this material shows a slow polymerization reaction.
Volumetric Shrinkage and Stress of Polymerization
SIL showed the lowest volumetric shrinkage than the tested methacrylate-based composite resins. The type of the polymerization reaction might be responsible for the reduction of shrinkage30. Cationic ring opening polymerization of the cycloaliphatic oxirane moieties would be the reason for silorane-based composites to show this result27. This result is in agreement with previous studies32,33.
VF showed the highest values of volumetric shrinkage and stress of polymerization. It could be related to the composition. VF is a self-adhering flowable composite that, by manufacturer, combines the resin technology of composites and adhesives into one step, needing neither etching nor a bonding agent21. The composition of VF is not totally known but to perform the function of adhesive this material contains glycerol phosphate dimethacrylate (GPDM) and low molecular weight methacrylate co-monomers, explicating high values to shrinkage and stress. Even presenting 70 wt% and 48 vol% of filler particles19, the influence of organic matrix looks to be stronger in the volumetric shrinkage and stress34.
In this instance, TEC and SDR bulk-fill composites presented similar results to Z100, a conventional composite. This is not in agreement with previous study to evaluate restorations in natural teeth and the TEC and SDR showed a significantly less volumetric shrinkage than the tested conventional composite35. The discrepancy between results might be related that in the previous study the materials were placed in situ in a class I cavity
20
preparation, using bonding agents and the evaluation was performed by micro-CT.
However, TEC, SDR and, Z100 showed different values of polymerization stress. These composites contain different filler particles volume (60 vol%, 44 vol% and, 66 vol%, respectively) and SDR, with the lowest volume, obtained the highest stress of polymerization. It can suggest that high filler particles levels are not efficient to reduce polymerization stress, what it is in agreement with other studies36,37. The lower values of stress of SDR compared with Z100 and TEC could be explained by its composition. SDR has a polymerization modulator chemically embedded in the resin monomer and it would be able to reduce stress build-up upon polymerization without a reduction in the polymerization rate or conversion10. According to the manufacturer, this component is responsible for more linear/branching chain propagation without much cross-linking, and hence slower modulus development. This modulating effect allows extended polymerization reaction without a sudden increase in cross-link density. The extended curing reaction maximizes the overall degree of conversion, what is in agreement with ours degree of conversion results, and minimizes the polymerization stress10.
5. Conclusion
The tested materials showed different behaviors in relation to physic-chemical properties:
1) SIL showed the lowest values for volumetric shrinkage and stress of polymerization; 2) The best flexural strength was showed by VF;
3) SDR obtained satisfactory performance in all tested properties.
Acknowledgments
The authors thank the funding agency CAPES (Process # 1577-12-3) Brazil and the dental companies listed in Table 1 are gratefully acknowledged for the generous donation of materials used for this study.
21
The authors of this manuscript certify that they have no proprietary, financial, or other personal interest of any nature or kind in any product, service, and/or company that is presented in this article.
References
1. Ferracane JL. Buonocore Lecture. Placing dental composites - a stressful experience. Oper Dent. 2008; 33(3): 243-53.
2. Ferracane JL. Resin Composite - State of the art. Dent Mater. 2011; 27(1): 29-38. 3. Ilie N, Hickel R. Investigations on a methacrylate-based flowable composite based
on the SDR™ technology. Dent Mater. 201; 27(4): 348-55.
4. Hanabusa M, Mine A, Kuboki T, Momoi Y, Van Landuyt KL, Van Meerbeek B, De Munck J. TEM interfacial characterization of an experimental self-adhesive filling material bonded to enamel/dentin. Dent Mater. 2011; 27(8): 818-24.
5. Peutzfeldt A. Resin composites in dentistry: the monomer systems. Eur J Oral Sci. 1997; 105(2): 97-116.
6. Bowen RL. Properties of a silica-reinforced polymer for dental restorations. J Am Dent Assoc. 1963; 66: 57-64.
7. Van Meerbeek B, De Munck J, Yoshida Y, Inoue S, Vargas M, Vijay P, Van Landuyt K, Lambrechts P, Vanherle G. Buonocore memorial lecture. Adhesion to enamel and dentin: current status and future challenges. Oper Dent. 2003; 28(3): 215-35.
8. Rengo C, Goracci C, Juloski J, Chieffi N, Giovannetti A, Vichi A, Ferrari M. Influence of phosphoric acid etching on microleakage of a self-etch adhesive and a self-adhering composite. Aust Dent J. 2012; 57(2): 220-6.
9. Czasch P, Ilie N. In vitro comparison of mechanical properties and degree of cure of bulk fill composites. Clin Oral Investig, 2012 Mar 14. [Epub ahead of print].
10. SureFil SDR Flow Technical Profile. [access 2014 dec 2]. Available in:
http://dentsplymea.com/sites/default/files/SDR_OPL_factfile_3p.pdf
11. Technical Profile de Tetric EvoCeram Bulk Fill. [acess 2014 dec 2]. Available in:
22
12. Boaro LC, Gonçalves F, Guimarães TC, Ferracane JL, Versluis A, Braga RR. Polymerization stress, shrinkage and elastic modulus of current low-shrinkage restorative composites. Dent Mater. 2010; 26(12): 1144-50.
13. Gonçalves F, Boaro LC, Ferracane JL, Braga RR. A comparative evaluation of polymerization stress data obtained with four different mechanical testing systems. Dent Mater. 2012; 28(6): 680-6. doi: 10.1016/j.dental.2012.03.004.
14. Bryant RW, Mahler DB. Volumetric contraction in some tooth-coloured restorative materials. Aust Dent J. 2007; 52(2): 112-7.
15. Howard B, Wilson ND, Newman SM, Pfeifer CS, Stansbury JW. Relationships between conversion, temperature and optical properties during composite photopolymerization. Acta Biomater. 2010; 6(6): 2053-9. doi: 10.1016/j.actbio.2009.11.006.
16. Leprince JG, Palin WM, Vanacker J, Sabbagh J, Devaux J, Leloup G. Physico-mechanical characteristics of commercially available bulk-fill composites. J Dent. 2014; 42(8): 993-1000. doi: 10.1016/j.jdent.2014.05.009.
17. Sabbagh J, Vreven J, Leloup G. Dynamic and static moduli of elasticity of resin-based materials. Dent Mater. 2002; 18(1): 64–71.
18. Leprince J, Palin WM, Mullier T, Devaux J, Vreven J, Leloup G. Investigating filler morphology and mechanical properties of new low-shrinkage resin composite types. J Oral Rehabil. 2010; 37(5): 364–76.
19. Vertise Flow Technical Bulletin. [acess 2014 dec 2]. Available in: http://www.kerrdental.com/cms-filesystem-action/KerrDental-products-techinfo/vertiseflow_techbulletin_34929b.pdf 20. El-Damanhoury H, Platt J. Polymerization shrinkage stress kinetics and related
properties of bulk-fill resin composites. Oper Dent. 2014; 39(4): 374-82. doi: 10.2341/13-017-L.
21. Leprince JG, Palin WM, Vanacker J, Sabbagh J, Devaux J, Leloup G. Physico-mechanical characteristics of commercially available bulk-fill composites. J Dent. 2014; 42(8): 993-1000. doi: 10.1016/j.jdent.2014.05.009.
22. Flury S, Peutzfeldt A, Lussi A. Influence of increment thickness on microhardness and dentin bond strength of bulk fill resin composites. Dent Mater. 2014; 30(10):
23 1104-12. doi: 10.1016/j.dental.2014.07.001.
23. Czasch P, Ilie N. In vitro comparison of mechanical properties and degree of cure of bulk fill composites. Clin Oral Investig. 2013; 17(1): 227-35. doi: 10.1007/s00784-012-0702-8.
24. E Asmussen, A. Peutzfeldt. Influence of UEDMA, BisGMA and TEGDMA on selected mechanical properties of experimental resin composites. Dent Mater. 1998; 14(1): 51–6.
25. Ilie N, Durner J. Polymerization kinetic calculations in dental composites: a method comparison analysis. Clin Oral Investig. 2014; 18(6): 1587-96. doi: 10.1007/s00784-013-1128-7.
26. Burtscher P. Stability of radicals in cured composite materials. Dent Mater. 1993; 9(4): 218-21.
27. Goracci C, Cadenaro M, Fontanive L, Giangrosso G, Juloski J, Vichi A, Ferrari M. Polymerization efficiency and flexural strength of low-stress restorative composites. Dent Mater. 2014; 30(6): 688-94. doi: 10.1016/j.dental.2014.03.006.
28. Finan L, Palin WM, Moskwa N, McGinley EL, Fleming GJ. The influence of irradiation potential on the degree of conversion and mechanical properties of two bulk-fill flowable RBC base materials. Dent Mater. 2013; 29(8): 906-12. doi: 10.1016/j.dental.2013.05.008.
29. Czasch P, Ilie N. In vitro comparison of mechanical properties and degree of cure of a self-adhesive and four novel flowable composites. J Adhes Dent. 2013; 15(3): 229-36. doi: 10.3290/j.jad.a29530.
30. Par M, Gamulin O, Marovic D, Klaric E, Tarle Z. Raman Spectroscopic Assessment of Degree of Conversion of Bulk-Fill Resin Composites - Changes at 24 Hours Post Cure. Oper Dent. 2014 Oct 2. [Epub ahead of print].
31. Odian, G. Principles of polymerization. 4th ed. New York: John Wiley & Sons; 2004.
32. Yamasaki LC, De Vito Moraes AG, Barros M, Lewis S, Francci C, Stansbury JW, Pfeifer CS. Polymerization development of "low-shrink" resin composites: Reaction kinetics, polymerization stress and quality of network. Dent Mater. 2013; 29(9):
24 e169-79. doi: 10.1016/j.dental.2013.04.021.
33. Karaman E, Ozgunaltay G. Polymerization shrinkage of different types of composite resins and microleakage with and without liner in class II cavities. Oper Dent. 2014; 39(3): 325-31. doi: 10.2341/11-479-L.
34. Ellakwa A, Cho N, Lee IB. The effect of resin matrix composition on the polymerization shrinkage and rheological properties of experimental dental composites. Dent Mater. 2007; 23(10): 1229-35.
35. Hirata R, Clozza E, Giannini M, Farrokhmanesh E, Janal M, Tovar N, Bonfante EA, Coelho PG. Shrinkage assessment of low shrinkage composites using micro-computed tomography. J Biomed Mater Res B Appl Biomater. 2014 Aug 13. doi: 10.1002/jbm.b.33258. [Epub ahead of print]
36. El-Damanhoury H, Platt J. Polymerization shrinkage stress kinetics and related properties of bulk-fill resin composites. Oper Dent. 2014; 39(4): 374-82. doi: 10.2341/13-017-L.
37. Ferracane JL. Developing a more complete understanding of stresses produced in dental composites during polymerization. Dent Mater. 2005; 21(1): 36-42.
25
CAPÍTULO 2
Microtensile bond strength and hardness in depth of materials and restorative technique combinations
Abstract
Objective: To evaluate hardness in depth of different composites classes and microtensile bond strength (µTBS) of Class II cavities filled by different restorative techniques and diverse materials association before and after mechanical fatigue-cycling test.
Materials and methods: Class II occluso-distal cavities (6 x 2 x 4 mm) in extracted human molars were restored using XP Bond (XP) etch-and-rinse adhesive system or silorane-based (SSA) associated to Z100 (Z100), Tetric EvoCeram Bulk Fill (TEC), Surefil SDR flow (SDR), Vertise Flow (VF), and Filtek Silorane (SIL) composites placed by incremental (I) or bulk (B) technique. The tested experimental groups were: XP-Z-B, XP-Z-I, SSA-Z-B, SSA-Z-I, XP-TEC-B, XP-TEC-I, XP-SDR-Z100, SSA-SDR-Z100, VF-Z-B and SSA-SIL-B (n=16). Half of the samples were prepared to obtain sticks and submitted to the µTSSA-SIL-BS test after 7 days of storage. The other samples were submitted to the mechanical fatigue-cycling test before the µTBS test. Hardness in depth was carried out in restorations with 4.0 mm of depth, removed, included in epoxy resin and submitted to Knoop hardness test (n=3). Results were statically analyzed by ANOVA and Tukey’s test (p<0.05).
Results: In relation to µTBS results in no-cycled groups, VF-Z-B exhibited the lowest values in occlusal and cervical surfaces (11.44 and 9.80 MPa, respectively), and XP-SDR-Z obtained the highest values in both tested surfaces (28.23 and 38.25 MPa). In cycled groups for the occlusal surface, the group SSA-SDR-Z obtained the lowest results (7.81 MPa), and XP-Z-I and XP-SDR-Z the highest results (23.24 and 21.48 MPa, respectively). To cervical surface, XP-TEC-B exhibited the lowest values (14.29 MPa) and XP-TEC-I and XP-SDR-Z the highest ones (33.15 and 31.90 MPa, respectively). The mechanical fatigue-cycling test affected significantly only the groups XP-TEC-I and SSA-SDR-Z. VF
26
obtained the lowest top-to-bottom ratio depth of cure results (0.66), while the other composites exhibited less than 20% of reduction.
Conclusion: Incremental technique not allow better bonding strength than bulk technique. The bulk-fill tested materials showed different performances. The combination between silorane-based and methacrylate-based materials did not appear to be promising. The self-adhering material (VF) showed unsatisfactory adhesion and depth of cure.
27 1. Introduction
During the polymerization of composite resins, the formation of a polymer network results in a denser structure, increasing the volumetric shrinkage1 and, consequently the shrinkage stress that can cause adhesive failures, cracks in the tooth structure, secondary caries and premature failure of restorations2. Furthermore, these composites require a surface pretreatment of enamel and dentin using either an etch-and-rise or self-etch adhesive making the placement of the materials more complex in a technique more sensitive3.
In order to simplify the clinical application and to reduce the technique sensitivity, the Vertise Flow4 (Kerr, Orange, USA) self-adhesive composite was introduced to the market as the first flowable resin composite. According to the manufacturer’s instructions, self-adhesive composites do not require any pretreatment of the substrate5 and its self-adhesiveness is based upon the use of acidic monomers that de-mineralizes and simultaneously infiltrates the tooth substrate, resulting in micro-mechanical retention, potential enhanced by additional chemical interaction5.
To minimize volumetric shrinkage and subsequent shrinkage stress, manufacturers have invested in the development of low-shrinkage restorative composites. Recently, an example of this new material (FiltekTM LS – Low Shrink Posterior) is available for clinical use6. According to manufacturer’s instructions, Filtek LS requires a specific self-etch adhesive system and can be placed in a bulk increment reducing the working time, volumetric shrinkage and stress7.
Bulk-fill composites, such as Tetric Evo-Ceram Bulk Fill and SureFill SDR Flow, have also been recently developed to reduce placement time and simplify the procedure. These materials are designed to be placed in 4 mm thick increments, without negatively affecting the mechanical and physical properties8.
The introduction of these new resin composites allows for an alteration in the restorative technique. Incremental layering has long been accepted as a standard technique for placement of resin-composite in cavity preparations9. This technique consists of placing increments of resin-composite material in thickness of 2 mm or less followed by exposure
28
to light curing from an occlusal direction and then repeating increments until the preparation is filled9,10. The advantages for this technique are adequate light penetration and subsequent polymerization resulting in enhanced physical and mechanical properties, decreased cytotoxicity11,12, and reduction of polymerization shrinkage stress13. But the incremental technique has disadvantages as the possibility of incorporating voids and contamination between composite layers, bond failures between increments, difficulty in placement because of limited access in conservative preparations, and the long time required to fill the cavity9, 14. Thus, the use of bulk-fill techniques is being encouraged because this would substantially simplify restorative procedures and reduce chair time15.
However, when incremental and bulk-fill techniques are compared, the results are conflicting. A study has reported that the incremental technique produces higher shrinkage stress and cuspal deflection14. In contrast, other studies have shown reduced cuspal deflection and higher resin-dentin micro-tensile bond strength with an incremental technique compared to bulk-fill technique in large cavities16,17. It should be noted that some of the difference in outcomes might be due to difference in curing protocols employed in these various studies.
The purpose of this study was to evaluate depth of cure and microtensile dentin bond strength of different combinations of materials and restorative techniques, including bulk fill and self-adhesive flowable composites. The hypotheses tested were:
(1) Microtensile bonding strength values would not be affect by the bonding agent; (2) Different restorative protocols would be similar in microtensile bond strength
performance;
(3) Different materials would not be affecting the bonding strength values; (4) Tested resin composites would show similar results for hardness in depth.
2. Materials and methods
29 Table 1: Materials used in this study.
Resin Composites (Abbreviation)
Organic Matrix Inorganic Filler Manufacturer and Batch No.
Z100 (Z100) Bis-GMA, TEGDMA, 2-benzotriazolylmethylphenol. Zirconia/sílica: 0.01-3.5µm 85%(wt) and 66% (vol). 3M ESPE N427925 Tetric EvoCeram Bulk Fill (TEC)
Dimethacrylate. Ba-glass, YbF3, mixoxide,
PPF 81%(wt) and 61%(vol).
Ivoclar Vivadent R49602
Surefil SDR flow (SDR)
Mod UDMA, EBPADMA, TEGDMA.
Ba-Al-F-B-Si glass, Sr-F-Si glass 68%(wt) and 45%(vol).
Dentsply 100506
Filtek Silorane Low Shrink Posterior Restorative (SIL) Silorane (3,4- epoxycyclohexylethylcyclo-polymethylsiloxane, bis3,4- epoxycyclohexylethyl-phenylmethylsilane).
Quartz radiopaque yttrium fluoride 76%(wt) and 50%(vol). 3M ESPE N436469 Vertise Flow (VF)
GPDM and HEMA Prepolymerized filler, barium glass filler, sized colloidal silica, nano-sized ytterbium fluoride 70%(wt) and 50%(vol).
Kerr Corporation 4675010
Adhesives (Abbreviation)
Composition Instructions for Use Manufacturer and Batch No. XP Bond Universal
Total Etch Adhesive (XP)
Etchant: Caulk 34% Tooth Conditioner Gel (34% phosphoric acid) Primer/Bond: TCB resin, PENTA, UDMA, TEGDMA, BHT, CQ, amorphous silica (0503004020), mixed with SCA (self-cure activator 041203)
Acid etch: 15 seconds, rinse for 15 seconds, blot excesso water using a cotton pellet, do not air-dry
Adhesive: Apply uniformly, wait for 20 seconds, dry air for 5 seconds, and 10 seconds of light curing
Dentsply 120113
